Friction element



April 30, 1963 J. O. SMiLEY FRICTION ELEMENT Original Filed July 6, 1956 INVEN TOR. JAMES 0. SMILEY ATTORNEY Delaware Original application ."iuly 6, 1956, Ser. No. 596,266, new Patent No. 2,973,842, dated Mar. '7, 1961. Divided and this application June 27, 1960, Ser. No. 39,028

(Ilaims. c1. 7s 2es This invention relates to friction elements and is particularly concerned with metallic friction elements for use in brakes, clutches and the like.

This application is a division of application Ser. No. 596,266, filed July 6, 1956, now Patent No. 2,836,089.

It is the main object of the invention to provide a friction element which has the desired frictional characteristics and yet is suificiently ductile and strong to permit attachment thereof to elements of a mechanical combination, for example, a brake or clutch.

In carrying out the above object, it is another object of the invention to provide a composite, laminated friction element having a sintered surface or layer which provides the desired friction and wear characteristics together with a coextensive layer of a different sintered metallic material which is relatively more ductile and stronger and which provides a medium for attaching the friction element to a machine element in the brake or clutch combination in either fiat or arcuate form.

Specifically, the invention is directed to a sintered, ferrous friction element which includes a friction layer having a substantial percentage of graphite, which friction layer is juxtaposed and coextensively bonded to a layer of a more ductile material such as a ferrous material having substantially less graphite therein whereby the element may be riveted or otherwise attached to an element of a brake or clutch combination through the more ductile layer and may also be conformed to some degree to the contour of the machine element.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein:

FIGURES 1 through 5 are diagrammatic views of one type of die which may be used to form the friction element as described herein in the several positions thereof during the filling and briquetting of a friction element; and,

FIGURE 6 is a view of the friction element, as produced by the method disclosed in FIGURES 1 through 5, attached to a brake shoe through the use of rivets.

Specifically referring to the drawings, an arcuate friction element of composite form may be made by the method and in the tools shown in FIGURES 1 through 5 which are progressive views of the briquetting die in various stages of the briquetting operation.

In FIGURE 1, the female portion of the die 20 is shown at 22. This includes a die cavity 24 which has therein a plunger or lower punch member 26. The upper surface of the punch member 26 is curved in conformation and in the first stage of the operation, is spaced slightly below the top of the die cavity 24 as noted in FIGURE 1. The upper punch or plunger 28 conforms substantially in shape to the complement of the lower punch 26 allowing for the increased radius of the upper surface of the element. With two punches in the position shown in FIGURE 1, metal powder is filled into the die cavity as shown in FIGURE 2 at 30. This powder is scraped off the top of the die to level the quantity thereof which is predetermined and, in this instance, is a mixture of the iron powder with about 2% graphite mixed therethrough. The next step of the process is to cause the lower punch member 26 to be retracted to the position shown in FIGURE 3. The metal powder layer 3,087,814 Patented Apr. 30, 1963 30 moves downwardly with the punch and thereby provides a cavity thereover as noted at 32. This cavity is predetermined in volume and is then filled with the friction mixture comprising the iron, graphite and molybdenum disulfide which is then leveled off into a layer 34 as shown in FIGURE 4. Finally, the upper punch 28 is caused to descend upon the powder mixture and the metal powder in the two layers is briquetted under substantial pressures, for example, in the neighborhood of 60,000-100,000 pounds per square inch, preferably 80,- 000 pounds per square inch whereupon the layers are compressed into coherent self-sustaining masses in coextensive relation to one another and particles of one layer are caused to intermingle with particles of the other layer at the interface which tends to create a strong mechanical bond therebetween.

It will be noted that due to the fact that the lower punch is curved during the first filling operation, the thickness of the lower layer varies from the center thereof where it is the thinnest to the ends thereof where it is the thickest. Similarly, the thickness of the friction layer varies inversely from the center where it is the thickest to the edges where it is the thinnest. This particular balance between the thicknesses of the layers is useful since the riveting of the shoe is carried out adjacent the ends thereof where the more ductile and stronger lower layer is preferably thicker.

The briquetted part, including the two layers as shown at 39 in FIGURE 5, is subsequently ejected from the die and placed in a sintering furnace where it is sintered at temperatures in the order of 1800" F. to 2000 F., preferably about 1900 F. for a period from 30 to 60 minutes and preferably about forty minutes in a nonoxidizing atmosphere which will be in equilibrium with the carbon content of the material being sintered. The element 39, after sintering, is preferably counter-bored so that rivets 48 may be used to attach the element to a brake shoe 40 wherein the strong metal layer 44 is the portion which supports the rivets 48. The present invention not only provides strength for the relatively brittle friction layer 42 but it also provides a small degree of bendability to the element whereby the element may be conformed to a brake shoe.

In FIGURE 6, a finished element 40 is shown including the compressed and sintered friction layer 42 and the compressed and sintered more ductile layer 44 wherein the element 40 is attached to an iron or steel brake shoe 46 through countersunk rivets 48.

Specifically, this invention is directed to a friction element utilizing a metallic friction surface 42 similar to that disclosed in Arnett and Ankeney appliction, Serial -No. 540,842, now abandoned, assigned to the assignee of this application, wherein the friction surface is substantially ferrous in nature with a high percentage of graphite in the order of 22% and about 4% molybdenum disulfide with the remainder iron. This material may be modified with controlled quantities of lead, copper or both. The material may also include some ceramic fric tion controlling elements, if desired.

Some specific formulations that have proved useful are as follows wherein the percentages noted are by weight. In all cases iron makes up the remainder of the formulation.

Graphite powder 20 20 25 20 20 22 20 20 Molybdenum disulphide powder.. 5 5 6 5 5 4 2 5 CopperpOWder 3 3 5 5 Lead powder 3 3 3 Ceramic (powdered clny) 1% Iron powder (reduced oxid remander In all the above formulations, the powdered materials are of a suitable size, for example, capable of passing through 150 to 250 mesh screen as selected although powders outside this range may be used insome cases as iswell-known in the art.

Fromthese formulations, it is apparent that the compositions of the friction layer may vary widely accord ing to the specific requirements of the friction elements in its operative environment. A specific type of iron powder in either layer is preferably a reduced iron oxide powder although useful articles may be made using other commercial iron powders such as electrolytic iron, Swedish sponge iron, etc.

'Itis also to be understood that the more ductile layer may include small additions of other metals without departing from the spirit of the invention, for example, copper may be used to advantage to influence dimensional change. during sintering as is well known in the art. Thus, copper, lead or other suitable additions may be added up to 10% to meet specific objectives.

In all cases, however, the friction element or layer'is lacking in ductility and strength and necessarily requires reinforcement to permit satisfactory attachment of the same to the operating elements of a brake.

In order to accomplish this reinforcement, a friction element as described above having a nominal thickness in the order of has bonded thereto a layer of a relatively more ductile metallic material in the thickness of about' This may vary as desired but the relation of thickness is preferred.

This more ductile material is preferably a soft iron powder (reduced iron. oxide 250 mesh is suitable) mixed with graphite in quantities of from 1 to 4% and preferably 2%. The graphite addition in this instance is of considerable importance since sufficient graphite must be added to the relatively ductile layer to produce growth characteristics substantially comparable to those inherent to thefriction layer. The graphite addition must also produce a condition within the relatively ductile layer so that the ductile layer and the friction layer will have substantially similar expansion characteristics upon ejection from the briquetting die. In other words, both of 'these'layers, upon compression, have a tendency to expand when the briquette is removed from the die and it is'apparent that if the combination of the two layers is to remain intact, that the expansion characteristics must be of'a reasonably similar degree.

By controlling the type and quantity of graphite in the relatively ductile layer, it is possible to create conditions-in this'layer-most favorable to briquetting and sintering in combination with the friction layer so that the two layers may be bonded during the sintering step without separation lby'lamination and, in fact, without app'reciable lamination tendency'characteristics due to differential dimensional change between the two layers. These factors are best arrived at by trial since the density of the graphite has an influence as well as the quantity thereof and, therefore, a suitable balance must be determined forthe' specific application asis well known in the art.

While the embodiments of the present invention as herein disclosed constitute preferred forms, it is to be understood that other forms might beadopted.

What is claimed is as follows:

him the method for making a rectilinear friction element for use as a clutch or brake, the steps comprising, filling a mold cavity with one metal powder mixture so that the top surface of said mixture is level with the top of the mold, moving the. bottom surface .of the mold cavity with the metal powder layer thereon downwardly to provide an additional cavity thereover, filling the additional cavity with another metal powder mixture so that the top surface of said mixture is level with the top of l said mold, 'briquetting simultaneously the two metal powder layers so formed for causing intermingling of the material in said layers at the interface with a punch having a curved surface similar to the curved surface of the bottom of said mold to provide a curved compact wherein the first mentioned layer increases in thickness from its center toward its end while the second mentioned layer decreases from the center toward its end, sintering the composite compact so formed under suitable conditions of time, temperature and atmosphere to provide a friction element having two coextensively bonded layers of porous metal.

2. A method for making a curved friction element having a strong metal support and a coextensive friction facing carried thereby, the steps comprising, filling a mold cavity with powder mixture including metal powder capable of forming a strong metal support wherein the bottom surface of the cavity has the curved shape desired in the completed element, leveling the powder without compacting for forming a flat top surface thereon, moving the bottom surface away from the top of the mold cavity for translating the metal powder downwardly and for leaving an additional cavity thereover, filling said additional cavity with powder mixture including metal powder which will ultimately form said friction facing, leveling said powder for presenting a uniform thickness layer, compressing said two powder layers concurrently from the top surface thereof with a punch having the same general curvature as the bottom surface of the mold for forming an integral, self sustaining two strata element wherein the materials in said two strata are intermingled at the interface, removing said element from the mold cavity and sintering the same under suitable conditions to form a friction element having a friction 'layer of uniform thickness supported by and bonded coextensively to a strong supporting layer which is thicker at theends than in the middle thereof.

-3. The method claimed in claim 2 wherein the frictionlayer includes high percentages of graphite while the supporting layer has relatively small percentages of graphlayer whereby rivets used to attach the element to a support bear on the supporting layer.

5. In a method for making'a laminated friction element having at least two layers of porous metal coextensively bonded throughout their juxtaposed surfaces, the steps comprising; filling a cavity in a mold with one metal powder mixture so that the top surface of said mixture is level with the top of the mold, moving the bottom surface of the mold cavity with the metal powder layer thereon downwardly to provide an additional cavity thereover, filling the additional cavity with another metal powder'mixture so that the top surface of said mixture is level with the top of said mold, briquetting simultaneously the two metal powder layers so formed under pressure sufficient to produce a self-sustaining compact and for causing intermingling of the metal powders in the layers at the interface, removing the compact for the mold cavity, and then sintering the composite compact so formed under suitable conditions of time, temperature and atmosphere for forming a laminated article having two coextensively bonded, juxtaposed layers of porous metal.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN THE METHOD FOR MAKING A RECTILINEAR FRICTION ELEMENT FOR USE A CLUTCH OR BRAKE, THE STEPS COMPRISING, FILLING A MOLD CAVITY WITH ONE METAL POWDER MIXTURE SO THAT THE TOP SURFACE OF SAID MIXTURE IS LEVEL WITH THE TOP OF THE MOLD, MOVING THE BOTTOM SURFACE OF THE MOLD CAVITY WITH THE METAL POWDER LAYER THEREON DOWNWARDLY TO PROVIDE AN ADDITIONAL CAVITY THEREOVER, FILLING THE ADDITIONAL CAVITY WITH ANOTHER METAL POWDER MIXTURE SO THAT THE TOP SURFACE OF SAID MIXTURE IS LEVEL WITH THE TOP OF SAID MOLD, BRIQUETTING SIMULTANEOUSLY THE TWO METAL POWDER LAYERS SO FORMED FOR CAUSING INTERMINGLING OF THE MATERIAL IN SAID LAYERS AT THE INTERFACE WITH A PUNCH HAVING A CURVED SURFACE SIMILAR TO THE CURVED SURFACE OF THE BOTTOM OF SAID MOLD TO PROVIDE A CURVED COMPACT WHERE IN THE FIRST MENTIONED LAYER INCREASES IN THICKNESS FROM ITS CENTER TOWARD ITS END WHILE THE SECOND MENTIONED LAYER DECREASES FROM THE CENTER TOWARD ITS END, SINTERING THE COMPOSITE COMPACT SO FORMED UNDER SUITABLE CONDITIONS OF TIME, TEMPERATURE AND ATMOSPHERE TO PROVIDE A FRICTION ELEMENT HAVING TWO COEXTENSIVELY BONDED LAYERS OF POROUS METAL. 